The antibiotic 'kanamycin' in the growing of culture E. coli I'm a first year student and I'm not sure if I understand correctly the role played by the antibiotic 'kanamycin' in the growing of culture E. coli (Rosetta). Can anybody explain me why we use 'kanamycin' antibiotic and kanamycin resistance gene during that process?

Absolutely, **Positive Selection**

You are looking for the bacteria which _have_ the gene (probably a plasmid) you (or someone else for you) put into the bacteria. That gene lets them live in the presence of kanamycin, and any bacteria that don't have it, or that try to get rid of it, will die. Thus you can select for the bacteria you want by killing everything else off (hopefully your sample is not contaminated with other bacteria also resistant to kanamycin).

I totally thought there would be a good wiki article on positive selection but there isn't. The reason it's positive selection is that you are selecting for bacteria that have something; instead of negative selection where you would be killing them for having something.

You can find plenty more if you search "positive selection" or more generally "artificial selection."